Nuclear magnetic resonance (NMR) spectroscopy is a technique that utilizes the magnetic properties of nuclei to obtain information about the physical, chemical, electronic and structural properties of molecules. When placed in a magnetic field, certain NMR active (such as 1H and 13C) are aligned with the field. This alignment can be perturbed using an alternating magnetic field that is generally orthogonal to the main field. The alternating magnetic field is typically administered by a radio frequency (RF) coil that is proximate the sample. After the alternating magnetic field is terminated, a signal can be collected by the RF coil due to a current induced in the RF coil as the nuclei in the sample “relax” or realign with the primary magnetic field.
NMR spectroscopy has been used to study living cells, which can be immobilized inside a semi-permeable encapsulate and suspended in a fluid. One potential difficulty in NMR spectroscopy is to maintain cells in a high density in the suspension for the amount of time desired to obtain a spectrum while maintaining the viability of the cells. The cells typically have relatively low NMR sensitivity, and consequently the cells may be placed in an NMR sample chamber with high concentrations in an effort to achieve higher NMR signals. However, it may be difficult to sustain the viability of living cells in the sufficiently high densities that may be desirable for high NMR signal strength.
NMR sample chambers have been developed in an effort to maintain a high density of cells to reduce signal acquisition times while also attempting to maintain cell viability. For example, NMR sample tubes have been designed to provide unidirectional flow of fluid, such as a perfusion medium including oxygen and/or glucose for maintaining cell viability. The fluid exits the sample tube through a filter, which is sized to generally prevent the cells from also exiting the sample tube. Although the fluid flow operates to compact the encapsulated cells in the NMR tube and supply oxygen and/or glucose, these systems may have problems associated with filter clogging. In addition, the encapsulated cells may be in such close proximity to one another that cell viability may be difficult to achieve.